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Motors
Motors Come in various types. * PMDC * Universal Motors ** Series and Shunt wound. * Single Phase AC ** Shaded Pole ** Split Phase (Capacitor Run/Start) * Three Phase AC ** Induction Motor ** Brushless DC DC and Universal Motors PMDC Permanent Magnet DC. Uses permanent magnets, a wound rotor (armature), and a pair of brushes and a commutator. The advantage of these motors is being relatively small and powerful, as well as being generally low-cost (for small motors), as well as being easy to run (connect power and go). Disadvantages are that it isn't really possible to (effectively) control speed independent of torque (if you reduce duty cycle in an H-bridge driver, both speed and torque are generally reduced). Another disadvantage is being unable to know how far the motor has traveled without external feedback (such as an encoder or potentiometer). Example common use cases are in toys and cordless power tools. They may also be used in robots and in electric scooters and similar. Series and Shunt Motors Like PMDC motors, these generally use brushes and an armature, but differ in that the permanent magnets are replaced with a wire-wound stator (external housing), which may be wired in either series or in parallel (shunt) with the armature. These stator coils then generate a magnetic field for the armature to interact with. Their primary advantage is that they can be run off AC power without needing to convert it to DC, but are generally bigger and less efficient than PMDC motors (and motors designed for AC power generally run like crap on DC, being both underpowered and running hot and/or burning up). A common use case is in AC-powered tools (drills, saws, vacuum cleaners, ...). Single Phase AC These are motors designed to run off of single-phase AC power. Generally these will not work if given raw DC (without an inverter). Shaded Pole Consist of a single or pair of comparably large coils, and a squirrel-cage induction rotor. These coils form an alternating magnetic field when given AC power. A small coil or copper ring is generally placed off to the side, which is induced by the main field and creates a secondary field out-of-phase with the first. The purpose of this field is to help the motor start spinning. Advantage is that they are comparably simple and low cost. Disadvantage is that they suck in nearly every other sense. Primary use case is in AC powered electric fans. Split Phase These consist of multiple sets of coils connected together via one or more capacitors. Like in the shaded pole motors, there is a single primary set of coils which is driven directly by AC power. Another set of weaker coils is driven by the capacitor, and is used to provide a rotating magnetic field. General advantage is that it has higher torque than a shaded pole motor (thus generally more useful, as it can actually drive a load). Likewise, it can run fairly directly off of AC power. It is generally easier to convert into a different type of motor (the rotor and stator may be reussed to make a 3-phase induction motor, unlike a shaded pole motor where generally the stator is pretty useless for anything else). Three Phase Motors Three Phase Induction Have generally a multiple of 3 stator coils (usually 6, but may be 9 or more), and a squirrel cage rotor. Advantage is that these motors are pretty useful and versatile. The main disadvantages is needing three-phase AC power, with many conventional three-phase motors assuming fairly high operating voltages (such as 208 or 440 volts). Brushless DC Generally these are the smaller sibling of the three-phase induction motor. The primary difference is that they tend to use permanent magnet rotors instead of a squirrel cage rotor. Another oddity is that many motors built in this style use an outrunner configuration, where the permanent magnet rotor spins around the outside of the stator. An advantage is that it is easier to know how far the motor has turned. A disadvantage is that under higher loads or under variable load, the motor may fall out of sync with the control signal. This will often cause the motor to "drop out" and lose all of its torque. A result of this is that generally dedicated hardware and software is needed to run them (they can be run open-loop, but generally this is less efficient and fairly load-dependent). Hybrid Three Phase A hybrid of a 3-Phase induction motor and BLDC. These designs generally have both an induction rotor and permanent magnets. They may be a single rotor (as shown here), or may involve use of multiple rotors connected via a clutch mechanism. This is considerably less common than the other motor types. Advantages are that synchronous operation is possible and that regenerative operation is easier. The motor will also not as easily drop out if things get out of sync. Disadvantages are cost and novelty, thus you wont generally find them.